This invention relates to thermal control paints, and, more particularly, to a black paint useful in spacecraft applications.
Spacecraft are subjected to a wide range of thermal environments during service. Heat radiates rapidly into free space to cool the spacecraft, but it can be heated intensively in direct sunlight. Active and passive temperature control techniques are used to control the interior temperature of the spacecraft, which contains persons or sensitive instruments. Active temperature control usually involves machinery or electrical devices, such as electrical heaters and air conditioners.
An established approach to passive temperature control is the use of surface coatings, typically termed paints, on the external surface of the spacecraft. A white paint, for example, has a low solar absorptance, while a black paint has a high emittance. The selective application of such paints to various elements of the spacecraft structure greatly aids in controlling its temperature. The present invention deals with a black paint that is useful in spacecraft temperature control applications.
A spacecraft paint, whatever its color, should exhibit additional characteristics for some spacecraft applications. The paint must be stable during long-term service in a space environment. It must be resistant to abrasion and other types of mechanical damage due to micrometeorite impacts. For some elements of the spacecraft, particularly those which deform such as a deployable antenna, a flexible blanket, or the like, the paint must also be tough and flexible so that it does not crack and flake away as it is flexed due to mechanical or thermal strains.
In most cases, the paint must dissipate electrostatic charges that develop on the external surface of the spacecraft. The charges would otherwise accumulate to cause arcing and possible damage to, or interference with, sensitive electronic equipment on or in the spacecraft. In order to dissipate electrostatic charge, the paint must be somewhat electrically conductive, with a surface resistivity on the order of about 10.sup.9 ohms per square or less.
There are black, electrostatic-dissipative paints known for spacecraft use. The available paints are satisfactory in applications where the temperature of the substrate to which they are applied remains relatively constant. However, none of these paints is fully satisfactory in applications where the substrate experiences a wide range of temperatures during service (e.g., -150.degree. C. to 200.degree. C.). Examples of spacecraft components experiencing such wide temperature ranges include flexible substrates such as mesh fabrics used in antennas. In particular, paints that are otherwise reasonably satisfactory in such applications tend to exhibit instability in the electrical resistivity during prolonged exposure in space. The result is that, after a period of time, the resistivity tends to increase so that the electrostatic charge is no longer dissipated, surface charges accumulate, and interference or damage may result.
There is a need for an improved black thermal-control paint, which would be of particular value in spacecraft applications which involve large temperature ranges, especially flexible mesh fabrics. The present invention fulfills this need, and further provides related advantages.